1. Field of the Invention
The present invention relates to an electronic image pickup apparatus and more specifically to a focus detecting unit applied to an electronic image pickup apparatus having image pickup devices for generating electrical image signals by photoelectrically converting an optical image of a subject formed by a photographic optical system.
2. Description of the Related Art
Various proposals have been made lately on electronic image pickup apparatuses such as a digital still camera and a digital video camera which are capable of photoelectrically converting an optical image of a subject formed of light beams which have been transmitted through a photographic optical system into electrical signals by utilizing image pickup devices such as CCDs (Charge Coupled Device) and of recording image signals generated therefrom to a recording medium or the like as image data of a predetermined mode.
For instance, Japanese Patent Laid-Open No. Hei. 8-262564 has disclosed a single-lens reflex type electronic image pickup apparatus constructed so as to be able to form an optical image to be photographed and recorded and an optical image for observation at different positions by using beams which have been transmitted through a single photographic optical system. This electronic image pickup apparatus is provided with image pickup means such as solid state image pickup devices on an image forming plane for picking up the image and image pickup means for detecting a focal point at the position equivalent to that image forming plane beside the image pickup means. The apparatus is arranged so as to carry out a focusing operation by a focus detecting means (AF means) using the TTL phase difference detecting method for detecting the focusing state of the optical image by guiding a part of the beams which have been transmitted through the photographic optical system to the focus detecting image pickup means.
An electronic image pickup apparatus disclosed in Japanese Patent Laid-Open No. Hei. 274130 is a so-called video movie camera for shooting and recording mainly video images. While it is provided with image pickup means such as image pickup devices disposed within the camera main body, a focusing detecting unit of the TTL phase difference detecting method comprising other image pickup means different from the image pickup means such as the image pickup devices is disposed with the inside of a lens barrel for holding camera lenses.
However, the prior art electronic image pickup apparatuses disclosed in Japanese Patent Laid-Open Nos. Hei. 8-262564 and 274130 comprise an image pickup means such as image pickup devices dedicated for detecting the focal point beside an image pickup means such as image pickup devices for shooting and recording an optical image.
Such a construction has caused problems that a number of parts of the whole electronic image pickup apparatus increases and the size of the apparatus itself increases. At the same time, because it requires a plurality of expensive parts such as the image pickup devices, it has caused a problem that the production cost also increases.